Pretreatment Compositions and Methods For Coating A Metal Substrate

ABSTRACT

Disclosed are pretreatment compositions and associated methods for treating metal substrates with pretreatment compositions, including ferrous substrates, such as cold rolled steel and electrogalvanized steel. The pretreatment composition includes: (a) a group IIIB and/or IVB metal; (b) free fluorine; (c) a source of aluminum ions; and (d) water. The methods include contacting the metal substrates with the pretreatment composition.

FIELD OF THE INVENTION

The present invention relates to pretreatment compositions and methodsfor coating a metal substrate, including ferrous substrates, such ascold rolled steel and electrogalvanized steel. The present inventionalso relates to coated metal substrates.

BACKGROUND INFORMATION

The use of protective coatings on metal substrates for improvedcorrosion resistance and paint adhesion is common. Conventionaltechniques for coating such substrates include techniques that involvepretreating the metal substrate with a phosphate conversion coating andchrome-containing rinses. The use of such phosphate and/orchromate-containing compositions, however, imparts environmental andhealth concerns.

As a result, chromate-free and/or phosphate-free pretreatmentcompositions have been developed. Such compositions are generally basedon chemical mixtures that in some way react with the substrate surfaceand bind to it to form a protective layer. For example, pretreatmentcompositions based on a group IIIB or IVB metal compound have recentlybecome more prevalent. Such compositions often contain a source of freefluorine, i.e., fluorine that is isolated in the pretreatmentcomposition as opposed to fluorine that is bound to another element,such as the group IIIB or IVB metal. Free fluorine can etch the surfaceof the metal substrate, thereby promoting deposition of a group IIIB orIVB metal coating. Nevertheless, the corrosion resistance capability ofthese pretreatment compositions has generally been significantlyinferior to conventional phosphate and/or chromium containingpretreatments.

As a result, it would be desirable to provide methods for treating ametal substrate that overcome at least some of the previously describeddrawbacks of the prior art, including the environmental drawbacksassociated with the use of chromates and/or phosphates. Moreover, itwould be desirable to provide methods for treating metal substrate that,in at least some cases, imparts corrosion resistance properties that areequivalent to, or even superior to, the corrosion resistance propertiesimparted through the use of phosphate conversion coatings. It would alsobe desirable to provide related coated metal substrates.

SUMMARY OF THE INVENTION

In certain respects, the present invention is directed to compositionsfor treating a metal substrate. These compositions comprise: (a) a groupIIIB and/or IVB metal; (b) an electropositive metal; (c) free fluorine;(d) a source of aluminum ions; and (e) water. The composition, incertain embodiments, is substantially free of heavy metal phosphate,such as zinc phosphate, and chromate. Moreover, the source of aluminumions is supplied in an amount sufficient to maintain the level of freefluorine in the composition to no less than 0.1 parts per million(“ppm”) and no more than 750 ppm.

In still other respects, the present invention is directed to methodsfor treating a metal substrate comprising cleaning the substrate andcontacting the substrate with a pretreatment composition comprising: (a)a group IIIB and/or IVB metal; (b) an electropositive metal; (c) freefluorine; (d) a source of aluminum ions; and (e) water, wherein theamount of aluminum ions supplied in an amount sufficient to maintain thelevel of free fluorine in the composition to no less than 0.1 ppm and nomore than 750 ppm.

The present invention is also directed to substrates treated thereby.

DETAILED DESCRIPTION OF THE INVENTION

For purposes of the following detailed description, it is to beunderstood that the invention may assume various alternative variationsand step sequences, except where expressly specified to the contrary.Moreover, other than in any operating examples, or where otherwiseindicated, all numbers expressing, for example, quantities ofingredients used in the specification and claims are to be understood asbeing modified in all instances by the term “about”. Accordingly, unlessindicated to the contrary, the numerical parameters set forth in thefollowing specification and attached claims are approximations that mayvary depending upon the desired properties to be obtained by the presentinvention. At the very least, and not as an attempt to limit theapplication of the doctrine of equivalents to the scope of the claims,each numerical parameter should at least be construed in light of thenumber of reported significant digits and by applying ordinary roundingtechniques.

Notwithstanding that the numerical ranges and parameters setting forththe broad scope of the invention are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value, however, inherently contains certainerrors necessarily resulting from the standard variation found in theirrespective testing measurements.

Also, it should be understood that any numerical range recited herein isintended to include all sub-ranges subsumed therein. For example, arange of “1 to 10” is intended to include all sub-ranges between (andincluding) the recited minimum value of 1 and the recited maximum valueof 10, that is, having a minimum value equal to or greater than 1 and amaximum value of equal to or less than 10.

In this application, the use of the singular includes the plural andplural encompasses singular, unless specifically stated otherwise. Inaddition, in this application, the use of “or” means “and/or” unlessspecifically stated otherwise, even though “and/or” may be explicitlyused in certain instances.

As previously mentioned, certain embodiments of the present inventionare directed to methods for treating a metal substrate. Suitable metalsubstrates for use in the present invention include those that are oftenused in the assembly of automotive bodies, automotive parts, and otherarticles, such as small metal parts, including fasteners, i.e., nuts,bolts, screws, pins, nails, clips, buttons, and the like. Specificexamples of suitable metal substrates include, but are not limited to,cold rolled steel, hot rolled steel, steel coated with zinc metal, zinccompounds, or zinc alloys, such as electrogalvanized steel, hot-dippedgalvanized steel, galvanealed steel, and steel plated with zinc alloy.Also, aluminum alloys, aluminum plated steel and aluminum alloy platedsteel substrates may be used. Other suitable non-ferrous metals includecopper and magnesium, as well as alloys of these materials. Moreover,the metal substrate being treated by the methods of the presentinvention may be a cut edge of a substrate that is otherwise treatedand/or coated over the rest of its surface. The metal substrate treatedin accordance with the methods of the present invention may be in theform of, for example, a sheet of metal or a fabricated part.

The substrate to be treated in accordance with the methods of thepresent invention may first be cleaned to remove grease, dirt, or otherextraneous matter. This is often done by employing mild or strongalkaline cleaners, such as are commercially available and conventionallyused in metal pretreatment processes. Examples of alkaline cleanerssuitable for use in the present invention include Chemkleen 163,Chemkleen 177, Chemkleen 490MX, Chemkleen 2010LP, Chemkleen 166 HP, andChemkleen 166 M, each of which are commercially available from PPGIndustries, Inc. Such cleaners are often followed and/or preceded by awater rinse.

Next, in some embodiments, an optional pre-rinse composition comprisingan electropositive metal is deposited onto at least a portion of themetal substrate. As used herein, the term “electropositive metal” refersto metals that are more electropositive than the metal substrate. Thismeans that, for purposes of the present invention, the term“electropositive metal” encompasses metals that are less easily oxidizedthan the metal of the metal substrate that is being treated. As will beappreciated by those skilled in the art, the tendency of a metal to beoxidized is called the oxidation potential, is expressed in volts, andis measured relative to a standard hydrogen electrode, which isarbitrarily assigned an oxidation potential of zero. The oxidationpotential for several elements is set forth in the table below. Anelement is less easily oxidized than another element if it has a voltagevalue, E*, in the following table, that is greater than the element towhich it is being compared.

Element Half-cell reaction Voltage, E* Potassium K⁺ + e → K −2.93Calcium Ca²⁺ + 2e → Ca −2.87 Sodium Na⁺ + e → Na −2.71 Magnesium Mg²⁺ +2e → Mg −2.37 Aluminum Al³⁺ + 3e → Al −1.66 Zinc Zn²⁺ + 2e → Zn −0.76Iron Fe²⁺ + 2e → Fe −0.44 Nickel Ni²⁺ + 2e → Ni −0.25 Tin Sn²⁺ + 2e → Sn−0.14 Lead Pb²⁺ + 2e → Pb −0.13 Hydrogen 2H⁺ + 2e → H₂ −0.00 CopperCu²⁺ + 2e → Cu 0.34 Mercury Hg₂ ²⁺ + 2e → 2Hg 0.79 Silver Ag⁺ + e → Ag0.80 Gold Au³⁺ + 3e → Au 1.50

Thus, as will be apparent, when the metal substrate comprises one of thematerials listed earlier, such as cold rolled steel, hot rolled steel,steel coated with zinc metal, zinc compounds, or zinc alloys, hot-dippedgalvanized steel, galvanealed steel, steel plated with zinc alloy,aluminum alloys, aluminum plated steel, aluminum alloy plated steel,magnesium and magnesium alloys, suitable electropositive metals fordeposition thereon include, for example, nickel, copper, silver, andgold, as well mixtures thereof.

As indicated, in certain embodiments of the present invention, anelectropositive metal is first deposited on the substrate. Any suitabletechnique may be used to accomplish this deposition, however, in certainembodiments, the deposition is accomplished without the use of electriccurrent. In particular, in certain embodiments, the electropositivemetal is deposited by contacting the substrate with a plating solutionof a soluble metal salt, such as a soluble copper salt, wherein themetal of the substrate dissolves while the metal in the solution, suchas copper, is plated out onto the substrate surface.

The plating solution referenced above is often an aqueous solution of awater soluble metal salt. In certain embodiments of the presentinvention, the water soluble metal salt is a water soluble coppercompound. Specific examples of water soluble copper compounds, which aresuitable for use in the present invention include, but are not limitedto, copper cyanide, copper potassium cyanide, copper sulfate, coppernitrate, copper pyrophosphate, copper thiocyanate, disodium copperethylenediaminetetraacetate tetrahydrate, copper bromide, copper oxide,copper hydroxide, copper chloride, copper fluoride, copper gluconate,copper citrate, copper lauroyl sarcosinate, copper formate, copperacetate, copper propionate, copper butyrate, copper lactate, copperoxalate, copper phytate, copper tartarate, copper malate, coppersuccinate, copper malonate, copper maleate, copper benzoate, coppersalicylate, copper aspartate, copper glutamate, copper fumarate, copperglycerophosphate, sodium copper chlorophyllin, copper fluorosilicate,copper fluoroborate and copper iodate, as well as copper salts ofcarboxylic acids in the homologous series formic acid to decanoic acid,copper salts of polybasic acids in the series oxalic acid to subericacid, and copper salts of hydroxycarboxylic acids, including glycolic,lactic, tartaric, malic and citric acids.

When copper ions supplied from such a water-soluble copper compound areprecipitated as an impurity in the form of copper sulfate, copper oxide,etc., it may be preferable to add a complexing agent that suppresses theprecipitation of copper ions, thus stabilizing them as a copper complexin the solution.

In certain embodiments, the copper compound is added as a copper complexsalt such as K₃Cu(CN)₄ or Cu-EDTA, which can be present stably in thecomposition on its own, but it is also possible to form a copper complexthat can be present stably in the composition by combining a complexingagent with a compound that is difficultly soluble on its own. Examplesthereof include a copper cyanide complex formed by a combination of CuCNand KCN or a combination of CuSCN and KSCN or KCN, and a Cu-EDTA complexformed by a combination of CuSO₄ and EDTA·2Na.

With regard to the complexing agent, a compound that can form a complexwith copper ions can be used; examples thereof include organiccompounds, such as cyanide compounds and thiocyanate compounds, andpolycarboxylic acids, and specific examples thereof includeethylenediaminetetraacetic acid, salts of ethylenediaminetetraaceticacid, such as dihydrogen disodium ethylenediaminetetraacetate dihydrate,aminocarboxylic acids, such as nitrilotriacetic acid and iminodiaceticacid, oxycarboxylic acids, such as citric acid and tartaric acid,succinic acid, oxalic acid, ethylenediaminetetramethylenephosphonicacid, and glycine.

In certain embodiments, the electropositive metal, such as copper, isincluded in the plating solution in an amount of at least 1 ppm, such asat least 50 ppm, or in some cases, at least 100 ppm of total metal(measured as elemental metal). In certain embodiments, theelectropositive metal, such as copper, is included in such platingsolutions in an amount of no more than 5000 ppm, such as no more than1000 ppm, or in some cases, no more than 500 ppm of total metal(measured as elemental metal). The amount of electropositive metal inthe plating solution can range between the recited values inclusive ofthe recited values.

In addition to the water soluble metal salt and optional complexingagent, the plating solution utilized in certain embodiments of thepresent invention may also include other additives. For example, astabilizer, such as an azole, such as 2-mercaptobenzothiazole, may beused. Other optional materials include surfactants that function asdefoamers or substrate wetting agents. Anionic, cationic, amphoteric, ornonionic surfactants may be used. Compatible mixtures of such materialsare also suitable. Defoaming surfactants are often present at levels upto 1 percent, such as up to 0.1 percent by volume, and wetting agentsare often present at levels up to 2 percent, such as up to 0.5 percentby volume, based on the total volume of the solution.

In certain embodiments, the aqueous plating solution utilized in certainembodiments of the present invention has a pH at application of lessthan 7, in some cases the pH is within the range of 1 to 6, such as 1.5to 5.5. In certain embodiments, the pH of the solution is maintainedthrough the inclusion of an acid. The pH of the solution may be adjustedusing mineral acids, such as hydrofluoric acid, fluoroboric acid andphosphoric acid, including mixtures thereof; organic acids, such aslactic acid, acetic acid, citric acid, sulfamic acid, or mixturesthereof; and water soluble or water dispersible bases, such as sodiumhydroxide, ammonium hydroxide, ammonia, or amines such as triethylamine,methylethyl amine, or mixtures thereof. The pH may also be adjustedusing inorganic acids such as, for example, sulfuric acid, hydrochloricacid, and/or nitric acid.

The plating solution may be brought into contact with the substrate byany of a variety of techniques, including, for example, dipping orimmersion, spraying, intermittent spraying, dipping followed byspraying, spraying followed by dipping, brushing, or roll-coating. Incertain embodiments, a dipping or immersion technique is used and thesolution, when applied to the metal substrate, is at a temperatureranging from 60 to 185° F. (15 to 85° C.). The contact time is oftenfrom 10 seconds to five minutes, such as 30 seconds to 2 minutes. Afterremoval of the substrate from the plating solution, the substrate may,if desired, be rinsed with water and dried.

In certain embodiments, the residue of the plating solution, i.e., theelectropositive metal, is present on the substrate in an amount rangingfrom 1 to 1000 milligrams per square meter (mg/m²), such as 10 to 400mg/m². The thickness of the residue of the plating solution can vary,but it is generally very thin, often having a thickness of less than 1micrometer, in some cases it is from 1 to 500 nanometers, and, in yetother cases, it is 10 to 300 nanometers.

In another alternative embodiment, the optional pre-rinse compositionmay comprise an acid cleaner solution without an electropositive metal.In certain embodiments, the acid cleaner solution utilized in certainembodiments of the present invention has a pH at application of lessthan 7, in some cases the pH is within the range of 1 to 6, such as 1.5to 5.5. The pH of the solution may be adjusted using mineral acids, suchas hydrofluoric acid, fluoroboric acid and phosphoric acid, includingmixtures thereof; organic acids, such as lactic acid, acetic acid,citric acid, sulfamic acid, or mixtures thereof; and water soluble orwater dispersible bases, such as sodium hydroxide, ammonium hydroxide,ammonia, or amines such as triethylamine, methylethyl amine, or mixturesthereof. The pH may also be adjusted using inorganic acids such as, forexample, sulfuric acid, hydrochloric acid, and/or nitric acid.

The acid cleaner solution may be brought into contact with the substrateby any of a variety of techniques, including, for example, dipping orimmersion, spraying, intermittent spraying, dipping followed byspraying, spraying followed by dipping, brushing, or roll-coating. Incertain embodiments, a dipping or immersion technique is used and thesolution, when applied to the metal substrate, is at a temperatureranging from 60 to 185° F. (15 to 85° C.). The contact time is oftenfrom 10 seconds to five minutes, such as 30 seconds to 2 minutes. Afterremoval of the substrate from the acid cleaner solution, the substratemay, if desired, be rinsed with water and dried.

Next, as previously indicated, certain embodiments of the presentinvention are directed to methods treating a metal substrate, with orwithout the optional pre-rinse, that comprise contacting the metalsubstrate with a pretreatment composition comprising a group IIIB and/orIVB metal. As used herein, the term “pretreatment composition” refers toa composition that, upon contact with the substrate, reacts with andchemically alters the substrate surface and binds to it to form aprotective layer.

Often, the pretreatment composition comprises a carrier, often anaqueous medium, so that the composition is in the form of a solution ordispersion of a group IIIB or IVB metal compound in the carrier. Inthese embodiments, the solution or dispersion may be brought intocontact with the substrate by any of a variety of known techniques, suchas dipping or immersion, spraying, intermittent spraying, dippingfollowed by spraying, spraying followed by dipping, brushing, orroll-coating. In certain embodiments, the solution or dispersion whenapplied to the metal substrate is at a temperature ranging from 60 to150° F. (15 to 65° C.). The contact time is often from 10 seconds tofive minutes, such as 30 seconds to 2 minutes.

As used herein, the term “group IIIB and/or IVB metal” refers to anelement that is in group IIIB or group IVB of the CAS Periodic Table ofthe Elements as is shown, for example, in the Handbook of Chemistry andPhysics, 63^(rd) edition (1983). Where applicable, the metal themselvesmay be used. In certain embodiments, a group IIIB and/or IVB metalcompound is used. As used herein, the term “group IIIB and/or IVB metalcompound” refers to compounds that include at least one element that isin group IIIB or group IVB of the CAS Periodic Table of the Elements.

In certain embodiments, the group IIIB and/or IVB metal compound used inthe pretreatment composition is a compound of zirconium, titanium,hafnium, yttrium, cerium, or a mixture thereof. Suitable compounds ofzirconium include, but are not limited to, hexafluorozirconic acid,alkali metal and ammonium salts thereof, ammonium zirconium carbonate,zirconyl nitrate, zirconium carboxylates and zirconium hydroxycarboxylates, such as hydrofluorozirconic acid, zirconium acetate,zirconium oxalate, ammonium zirconium glycolate, ammonium zirconiumlactate, ammonium zirconium citrate, and mixtures thereof. Suitablecompounds of titanium include, but are not limited to, fluorotitanicacid and its salts. A suitable compound of hafnium includes, but is notlimited to, hafnium nitrate. A suitable compound of yttrium includes,but is not limited to, yttrium nitrate. A suitable compound of ceriumincludes, but is not limited to, cerous nitrate.

In certain embodiments, the group IIIB and/or IVB metal compound ispresent in the pretreatment composition in an amount of at least 10 ppmmetal, such as at least 25 ppm metal, or, in some cases, at least 100ppm metal (measured as elemental metal). In certain embodiments, thegroup IIIB and/or IVB metal compound is present in the pretreatmentcomposition in an amount of no more than 5000 ppm metal, such as no morethan 300 ppm metal, or, in some cases, no more than 250 ppm metal(measured as elemental metal). The amount of group IIIB and/or IVB metalin the pretreatment composition can range between the recited valuesinclusive of the recited values.

In certain embodiments, the pretreatment composition also comprises anelectropositive metal, such as copper. The source of electropositivemetal, such as copper, in the pretreatment composition may comprise, forexample, any of the materials described earlier with respect to theplating solution. In certain embodiments, the electropositive metal,such as copper, is included in the pretreatment compositions in anamount of at least 1 ppm, such as at least 5 ppm, or in some cases, atleast 10 ppm of total metal (measured as elemental metal). In certainembodiments, the electropositive metal is included in such pretreatmentcompositions in an amount of no more than 500 ppm, such as no more than300 ppm, or in some cases, no more than 50 ppm of total metal (measuredas elemental metal). The amount of electropositive metal in thepretreatment composition can range between the recited values inclusiveof the recited values.

The pretreatment compositions of the present invention also comprisefree fluorine. As will be appreciated, the source of free fluorine inthe pretreatment compositions of the present invention can vary. Forexample, in some cases, the free fluorine may derive from the group IIIBand/or IVB metal compound used in the pretreatment composition, such asis the case, for example, with hexafluorozirconic acid. As the groupIIIB and/or IVB metal is deposited upon the metal substrate during thepretreatment process, fluorine in the hexafluorozirconic acid willbecome free fluorine and, as will be appreciated, the level of freefluorine in the pretreatment composition will, if left unchecked,increase with time as metal is pretreated with the pretreatmentcomposition of the present invention.

In addition, the source of free fluorine in the pretreatmentcompositions of the present invention may include a compound other thanthe group IIIB and/or IVB metal compound. Non-limiting examples of suchsources include HF, NH₄F, NH₄F, NH₄HF₂, NaF, and NaHF₂.

As used herein, the term “free fluorine” refers to isolated fluorine ionand its concentration in the pretreatment compositions of the presentinvention can be determined by measuring a pretreatment composition by ameter with a fluorine ion electrode. The Examples herein illustrate asuitable method for determining the concentration of free fluorine in acomposition for purposes of the present invention.

The pretreatment compositions of the present invention also comprise asource of aluminum ions. Moreover, in the compositions of the presentinvention, the amount of aluminum ions in the source of aluminum ions isselected such that the level of free fluorine in the composition is noless than 0.1 ppm, in some cases no less than 20 ppm, and no more than750 ppm, in some cases no more than 300 ppm. As will be appreciated, andas was previously mentioned, the level of free fluorine in thepretreatment compositions of the present invention will increase overtime as metal is pretreated therewith. In the present invention, thesource of aluminum ions as described above is supplied to thepretreatment composition as needed to maintain the level of freefluorine at no less than 0.1 ppm and no more than 750 ppm in thepretreatment composition.

Exemplary sources for aluminum ions that may be used include aluminumcompounds that are soluble in the water component of the pretreatmentcomposition (i.e. a water soluble aluminum compound). Such water solublealuminum compounds include aluminum sulfate, ammonium aluminum sulfate,potassium aluminum sulfate, sodium aluminum sulfate, aluminum nitrate,aluminum chloride, aluminum acetate, aluminum citrate, aluminum bromide,aluminum bromate, aluminum lactate, aluminum chlorate, aluminumtartrate, aluminum thiocyanate, aluminum hydroxychloride, aluminumformate, aluminum hydroxyacetate, aluminum malate, aluminum succinate,aluminum gluconate, aluminum glutamate, aluminum glycinate, aluminumfumarate, and their respective hydrated forms.

Another exemplary source for aluminum ions are aluminum compounds oflimited solubility in the water component of the pretreatmentcomposition but nevertheless may be able to provide aluminum ion undersome circumstances. Exemplary aluminum compounds having limitedsolubility in water but may be utilized include aluminum oxide, aluminumhydroxide, aluminum ferricyanide, aluminum phosphate, aluminum silicate,various aluminum-containing clays and zeolites, various aluminum soapsand salts of fatty acids.

In certain embodiments, a compound that can form a complex with thesource of aluminum ions can be used. The complexed aluminum is thenadded to the pretreatment composition. Examples of these complexingcompounds include organic compounds such as polycarboxylic acids and/oraminocarboxylic acids. Examples of suitable polycarboxylic acids thatmay be used in the present invention include oxycarboxylic acids, suchas citric acid and tartaric acid, succinic acid, oxalic acid,ethylenediaminetetramethylenephosphonic acid, and glycine. Examples ofsuitable aminocarboxylic acids that may be used in the present inventioninclude ethylenediaminetetraacetic acid, salts ofethylenediaminetetraacetic acid, such as dihydrogen disodiumethylenediaminetetraacetate dihydrate, aminocarboxylic acids, such asnitrilotriacetic acid and iminodiacetic acid, oxycarboxylic acids, suchas citric acid and tartaric acid, succinic acid, oxalic acid,ethylenediaminetetramethylenephosphonic acid, and glycine.

In certain embodiments, the pH of the pretreatment composition rangesfrom 2.0 to 7.0, such as 3.5 to 5,5. The pH of the pretreatmentcomposition may be adjusted using, for example, any acid or base as isnecessary. In certain embodiments, the pH of the solution is maintainedthrough the inclusion of a basic material, including water solubleand/or water dispersible bases, such as sodium hydroxide, sodiumcarbonate, potassium hydroxide, ammonium hydroxide, ammonia, and/oramines such as triethylamine, methylethyl amine, or mixtures thereof.

In certain embodiments, the pretreatment composition comprises aresinous binder. Suitable resins include reaction products of one ormore alkanolamines and an epoxy-functional material containing at leasttwo epoxy groups, such as those disclosed in U.S. Pat. No. 5,653,823. Insome cases, such resins contain beta hydroxy ester, imide, or sulfidefunctionality, incorporated by using dimethylolpropionic acid,phthalimide, or mercaptoglycerine as an additional reactant in thepreparation of the resin. Alternatively, the reaction product is that ofthe diglycidyl ether of Bisphenol A (commercially available from ShellChemical Company as EPON 880), dimethylol propionic acid, anddiethanolamine in a 0.6 to 5.0:0.05 to 5.5:1 mole ratio. Other suitableresinous binders include water soluble and water dispersible polyacrylicacids as disclosed in U.S. Pat. Nos. 3,912,548 and 5,328,525; phenolformaldehyde resins as described in U.S. Pat. No. 5,662,746; watersoluble polyamides such as those disclosed in WO 95/33869; copolymers ofmaleic or acrylic acid with allyl ether as described in Canadian patentapplication 2,087,352; and water soluble and dispersible resinsincluding epoxy resins, aminoplasts, phenol-formaldehyde resins,tannins, and polyvinyl phenols as discussed in U.S. Pat. No. 5,449,415.

In these embodiments of the present invention, the resinous binder ispresent in the pretreatment composition in an amount of 0.005 percent to30 percent by weight, such as 0.5 to 3 percent by weight, based on thetotal weight of the ingredients in the composition.

In other embodiments, however, the pretreatment composition issubstantially free or, in some cases, completely free of any resinousbinder. As used herein, the term “substantially free”, when used withreference to the absence of resinous binder in the pretreatmentcomposition, means that any resinous binder is present in thepretreatment composition in an amount of less than 0.005 percent byweight. As used herein, the term “completely free” means that there isno resinous binder in the pretreatment composition at all.

The pretreatment composition may optionally contain other materials,such as nonionic surfactants and auxiliaries conventionally used in theart of pretreatment. In an aqueous medium, water dispersible organicsolvents, for example, alcohols with up to about 8 carbon atoms, such asmethanol, isopropanol, and the like, may be present; or glycol etherssuch as the monoalkyl ethers of ethylene glycol, diethylene glycol, orpropylene glycol, and the like. When present, water dispersible organicsolvents are typically used in amounts up to about ten percent byvolume, based on the total volume of aqueous medium.

Other optional materials include surfactants that function as defoamersor substrate wetting agents.

In certain embodiments, the pretreatment composition also comprises areaction accelerator, such as nitrite ions, nitrate ions, nitro-groupcontaining compounds, hydroxylamine sulfate, persulfate ions, sulfiteions, hyposulfite ions, peroxides, iron (III) ions, citric acid ironcompounds, bromate ions, perchlorinate ions, chlorate ions, chloriteions as well as ascorbic acid, citric acid, tartaric acid, malonic acid,succinic acid and salts thereof. Specific examples of suitable materialsand their amounts are described in United States Patent ApplicationPublication No. 2004/0163736 A1 at [0032] to [0041], the cited portionof which being incorporated herein by reference.

In certain embodiments, the pretreatment composition also comprisesfiller, such as siliceous filler. Non-limiting examples of suitablefillers include silica, mica, montmorillonite, kaolinite, asbestos,talc, diatomaceous earth, vermiculite, natural and synthetic zeolites,cement, calcium silicate, aluminum silicate, sodium aluminum silicate,aluminum polysilicate, alumina silica gels, and glass particles. Inaddition to the siliceous fillers other finely divided particulatesubstantially water-insoluble fillers may also be employed. Examples ofsuch optional fillers include carbon black, charcoal, graphite, titaniumoxide, iron oxide, copper oxide, zinc oxide, antimony oxide, zirconia,magnesia, alumina, molybdenum disulfide, zinc sulfide, barium sulfate,strontium sulfate, calcium carbonate, and magnesium carbonate.

In certain embodiments, the pretreatment composition comprises phosphateions. In certain embodiments, phosphate ions are present in an amount of1 to 500 ppm of phosphate ion, such as 10 to 200 ppm phosphate ion.Exemplary sources of phosphate ion include H₃PO₄, NaH₂PO₄, and/or(NH₄)H₂PO₄. In certain embodiments, however, the pretreatmentcomposition of the present invention is substantially or, in some cases,completely free of phosphate ion. As used herein, the term“substantially free” when used in reference to the absence of phosphateion in the pretreatment composition, means that phosphate ion is presentin the composition in an amount less than 10 ppm. As used herein, theterm “completely free”, when used with reference to the absence ofphosphate ions, means that there are no phosphate ions in thecomposition at all. In certain embodiments, the pretreatment compositionis substantially or, in some cases, completely free of chromate and/orheavy metal phosphate, such as zinc phosphate. As used herein, the term“substantially free” when used in reference to the absence of chromateand/or heavy metal phosphate in the pretreatment composition, means thatthese substances are not present in the composition to such an extentthat they cause a burden on the environment. That is, they are notsubstantially used and the formation of sludge, such as zinc phosphate,formed in the case of using a treating agent based on zinc phosphate, iseliminated. As used herein, the term “completely free”, when used withreference to the absence of a heavy metal phosphate and/or chromate,means that there is no heavy metal phosphate and/or chromate in thecomposition at all.

Moreover, in certain embodiments, the pretreatment composition issubstantially free, or, in some cases, completely free of any organicmaterials. As used herein, the term “substantially free”, when used withreference to the absence of organic materials in the composition, meansthat any organic materials are present in the composition, if at all, asan incidental impurity. In other words, the presence of any organicmaterial does not affect the properties of the composition. As usedherein, the term “completely free”, when used with reference to theabsence of organic material, means that there is no organic material inthe composition at all.

In certain embodiments, the film coverage of the residue of thepretreatment coating composition generally ranges from 1 to 1000milligrams per square meter (mg/m²), such as 10 to 400 mg/m². Thethickness of the pretreatment coating can vary, but it is generally verythin, often having a thickness of less than 1 micrometer, in some casesit is from 1 to 500 nanometers, and, in yet other cases, it is 10 to 300nanometers.

Following contact with the pretreatment solution, the substrateoptionally may be rinsed with water and dried.

Optionally, after the pretreatment step, the substrate may then becontacted with a post-rinse solution. Post-rinse solutions, in general,utilize certain solubilized metal ions or other inorganic materials(such as phosphates or simple or complex fluorides) to enhance thecorrosion protection of pretreated metal substrates. These post-rinsesolutions may be chrome containing or non-chrome containing post-rinsesolutions. Suitable non-chrome post-rinse solutions that may be utilizedin the present invention are disclosed in U.S. Pat. Nos. 5,653,823;5,209,788; and 5,149,382; all assigned to PPG Industries, Inc. andherein incorporated by reference. In addition, organic materials(resinous or otherwise) such as phosphitized epoxies, base-solubilized,carboxylic acid containing polymers, at least partially neutralizedinterpolymers of hydroxyl-alkyl esters of unsaturated carboxylic acids,and amine salt-group containing resins (such as acid-solubilizedreaction products of polyepoxides and primary or secondary amines) mayalso be utilized alone or in combination with solubilized metal ionsand/or other inorganic materials.

After the optional post-rinse (when utilized), the substrate may berinsed with water prior to subsequent processing.

In certain embodiments of the methods of the present invention, afterthe substrate is contacted with the pretreatment composition, it is thencontacted with a coating composition comprising a film-forming resin.Any suitable technique may be used to contact the substrate with such acoating composition, including, for example, brushing, dipping, flowcoating, spraying and the like. In certain embodiments, however, asdescribed in more detail below, such contacting comprises anelectrocoating step wherein an electrodepositable composition isdeposited onto the metal substrate by electrodeposition.

As used herein, the term “film-forming resin” refers to resins that canform a self-supporting continuous film on at least a horizontal surfaceof a substrate upon removal of any diluents or carriers present in thecomposition or upon curing at ambient or elevated temperature.Conventional film-forming resins that may be used include, withoutlimitation, those typically used in automotive OEM coating compositions,automotive refinish coating compositions, industrial coatingcompositions, architectural coating compositions, coil coatingcompositions, and aerospace coating compositions, among others.

In certain embodiments, the coating composition comprises athermosetting film-forming resin. As used herein, the term“thermosetting” refers to resins that “set” irreversibly upon curing orcrosslinking, wherein the polymer chains of the polymeric components arejoined together by covalent bonds. This property is usually associatedwith a cross-linking reaction of the composition constituents ofteninduced, for example, by heat or radiation. Curing or crosslinkingreactions also may be carried out under ambient conditions. Once curedor crosslinked, a thermosetting resin will not melt upon the applicationof heat and is insoluble in solvents. In other embodiments, the coatingcomposition comprises a thermoplastic film-forming resin. As usedherein, the term “thermoplastic” refers to resins that comprisepolymeric components that are not joined by covalent bonds and therebycan undergo liquid flow upon heating and are soluble in solvents.

As previously indicated, in certain embodiments, the substrate iscontacted with a coating composition comprising a film-forming resin byan electrocoating step wherein an electrodepositable composition isdeposited onto the metal substrate by electrodeposition. In the processof electrodeposition, the metal substrate being treated, serving as anelectrode, and an electrically conductive counter electrode are placedin contact with an ionic, electrodepositable composition. Upon passageof an electric current between the electrode and counter electrode whilethey are in contact with the electrodepositable composition, an adherentfilm of the electrodepositable composition will deposit in asubstantially continuous manner on the metal substrate.

Electrodeposition is usually carried out at a constant voltage in therange of from 1 volt to several thousand volts, typically between 50 and500 volts. Current density is usually between 1.0 ampere and 15 amperesper square foot (10.8 to 161.5 amperes per square meter) and tends todecrease quickly during the electrodeposition process, indicatingformation of a continuous self-insulating film.

The electrodepositable composition utilized in certain embodiments ofthe present invention often comprises a resinous phase dispersed in anaqueous medium wherein the resinous phase comprises: (a) an activehydrogen group-containing ionic electrodepositable resin, and (b) acuring agent having functional groups reactive with the active hydrogengroups of (a).

In certain embodiments, the electrodepositable compositions utilized incertain embodiments of the present invention contain, as a mainfilm-forming polymer, an active hydrogen-containing ionic, oftencationic, electrodepositable resin. A wide variety of electrodepositablefilm-forming resins are known and can be used in the present inventionso long as the polymers are “water dispersible,” i.e., adapted to besolubilized, dispersed or emulsified in water. The water dispersiblepolymer is ionic in nature, that is, the polymer will contain anionicfunctional groups to impart a negative charge or, as is often preferred,cationic functional groups to impart a positive charge.

Examples of film-forming resins suitable for use in anionicelectrodepositable compositions are base-solubilized, carboxylic acidcontaining polymers, such as the reaction product or adduct of a dryingoil or semi-drying fatty acid ester with a dicarboxylic acid oranhydride; and the reaction product of a fatty acid ester, unsaturatedacid or anhydride and any additional unsaturated modifying materialswhich are further reacted with polyol. Also suitable are the at leastpartially neutralized interpolymers of hydroxy-alkyl esters ofunsaturated carboxylic acids, unsaturated carboxylic acid and at leastone other ethylenically unsaturated monomer. Still another suitableelectrodepositable film-forming resin comprises an alkyd-aminoplastvehicle, i.e., a vehicle containing an alkyd resin and an amine-aldehyderesin. Yet another anionic electrodepositable resin compositioncomprises mixed esters of a resinous polyol, such as is described inU.S. Pat. No. 3,749,657 at col. 9, lines 1 to 75 and col. 10, lines 1 to13, the cited portion of which being incorporated herein by reference.Other acid functional polymers can also be used, such as phosphatizedpolyepoxide or phosphatized acrylic polymers as are known to thoseskilled in the art.

As aforementioned, it is often desirable that the activehydrogen-containing ionic electrodepositable resin (a) is cationic andcapable of deposition on a cathode. Examples of such cationicfilm-forming resins include amine salt group-containing resins, such asthe acid-solubilized reaction products of polyepoxides and primary orsecondary amines, such as those described in U.S. Pat. Nos. 3,663,389;3,984,299; 3,947,338; and 3,947,339. Often, these amine saltgroup-containing resins are used in combination with a blockedisocyanate curing agent. The isocyanate can be fully blocked, asdescribed in U.S. Pat. No. 3,984,299, or the isocyanate can be partiallyblocked and reacted with the resin backbone, such as is described inU.S. Pat. No. 3,947,338. Also, one-component compositions as describedin U.S. Pat. No. 4,134,866 and DE-OS No. 2,707,405 can be used as thefilm-forming resin. Besides the epoxy-amine reaction products,film-forming resins can also be selected from cationic acrylic resins,such as those described in U.S. Pat. Nos. 3,455,806 and 3,928,157.

Besides amine salt group-containing resins, quaternary ammonium saltgroup-containing resins can also be employed, such as those formed fromreacting an organic polyepoxide with a tertiary amine salt as describedin U.S. Pat. Nos. 3,962,165; 3,975,346; and 4,001,101. Examples of othercationic resins are ternary sulfonium salt group-containing resins andquaternary phosphonium salt-group containing resins, such as thosedescribed in U.S. Pat. Nos. 3,793,278 and 3,984,922, respectively. Also,film-forming resins which cure via transesterification, such asdescribed in European Application No. 12463 can be used. Further,cationic compositions prepared from Mannich bases, such as described inU.S. Pat. No. 4,134,932, can be used.

In certain embodiments, the resins present in the electrodepositablecomposition are positively charged resins which contain primary and/orsecondary amine groups, such as described in U.S. Pat. Nos. 3,663,389;3,947,339; and 4,116,900. In U.S. Pat. No. 3,947,339, a polyketiminederivative of a polyamine, such as diethylenetriamine ortriethylenetetraamine, is reacted with a polyepoxide. When the reactionproduct is neutralized with acid and dispersed in water, free primaryamine groups are generated. Also, equivalent products are formed whenpolyepoxide is reacted with excess polyamines, such asdiethylenetriamine and triethylenetetraamine, and the excess polyaminevacuum stripped from the reaction mixture, as described in U.S. Pat.Nos. 3,663,389 and 4,116,900.

In certain embodiments, the active hydrogen-containing ionicelectrodepositable resin is present in the electrodepositablecomposition in an amount of 1 to 60 percent by weight, such as 5 to 25percent by weight, based on total weight of the electrodeposition bath.

As indicated, the resinous phase of the electrodepositable compositionoften further comprises a curing agent adapted to react with the activehydrogen groups of the ionic electrodepositable resin. For example, bothblocked organic polyisocyanate and aminoplast curing agents are suitablefor use in the present invention, although blocked isocyanates are oftenpreferred for cathodic electrodeposition.

Aminoplast resins, which are often the preferred curing agent foranionic electrodeposition, are the condensation products of amines oramides with aldehydes. Examples of suitable amine or amides aremelamine, benzoguanamine, urea and similar compounds. Generally, thealdehyde employed is formaldehyde, although products can be made fromother aldehydes, such as acetaldehyde and furfural. The condensationproducts contain methylol groups or similar alkylol groups depending onthe particular aldehyde employed. Often, these methylol groups areetherified by reaction with an alcohol, such as a monohydric alcoholcontaining from 1 to 4 carbon atoms, such as methanol, ethanol,isopropanol, and n-butanol. Aminoplast resins are commercially availablefrom American Cyanamid Co. under the trademark CYMEL and from MonsantoChemical Co. under the trademark RESIMENE.

The aminoplast curing agents are often utilized in conjunction with theactive hydrogen containing anionic electrodepositable resin in amountsranging from 5 percent to 60 percent by weight, such as from 20 percentto 40 percent by weight, the percentages based on the total weight ofthe resin solids in the electrodepositable composition.

As indicated, blocked organic polyisocyanates are often used as thecuring agent in cathodic electrodeposition compositions. Thepolyisocyanates can be fully blocked as described in U.S. Pat. No.3,984,299 at col. 1, lines 1 to 68, col. 2, and col. 3, lines 1 to 15,or partially blocked and reacted with the polymer backbone as describedin U.S. Pat. No. 3,947,338 at col. 2, lines 65 to 68, col. 3, and col. 4lines 1 to 30, the cited portions of which being incorporated herein byreference. By “blocked” is meant that the isocyanate groups have beenreacted with a compound so that the resultant blocked isocyanate groupis stable to active hydrogens at ambient temperature but reactive withactive hydrogens in the film forming polymer at elevated temperaturesusually between 90° C. and 200° C.

Suitable polyisocyanates include aromatic and aliphatic polyisocyanates,including cycloaliphatic polyisocyanates and representative examplesinclude diphenylmethane-4,4′-diisocyanate (MDI), 2,4- or 2,6-toluenediisocyanate (TDI), including mixtures thereof, p-phenylenediisocyanate, tetramethylene and hexamethylene diisocyanates,dicyclohexylmethane-4,4′-diisocyanate, isophorone diisocyanate, mixturesof phenylmethane-4,4′-diisocyanate and polymethylenepolyphenylisocyanate. Higher polyisocyanates, such as triisocyanates canbe used. An example would includetriphenylmethane-4,4′,4″-triisocyanate. Isocyanate ( )-prepolymers withpolyols such as neopentyl glycol and trimethylolpropane and withpolymeric polyols such as polycaprolactone diols and triols (NCO/OHequivalent ratio greater than 1) can also be used.

The polyisocyanate curing agents are typically utilized in conjunctionwith the active hydrogen containing cationic electrodepositable resin inamounts ranging from 5 percent to 60 percent by weight, such as from 20percent to 50 percent by weight, the percentages based on the totalweight of the resin solids of the electrodepositable composition.

In certain embodiments, the coating composition comprising afilm-forming resin also comprises yttrium. In certain embodiments,yttrium is present in such compositions in an amount from 10 to 10,000ppm, such as not more than 5,000 ppm, and, in some cases, not more than1,000 ppm, of total yttrium (measured as elemental yttrium).

Both soluble and insoluble yttrium compounds may serve as the source ofyttrium. Examples of yttrium sources suitable for use in lead-freeelectrodepositable coating compositions are soluble organic andinorganic yttrium salts such as yttrium acetate, yttrium chloride,yttrium formate, yttrium carbonate, yttrium sulfamate, yttrium lactateand yttrium nitrate. When the yttrium is to be added to an electrocoatbath as an aqueous solution, yttrium nitrate, a readily availableyttrium compound, is a preferred yttrium source. Other yttrium compoundssuitable for use in electrodepositable compositions are organic andinorganic yttrium compounds such as yttrium oxide, yttrium bromide,yttrium hydroxide, yttrium molybdate, yttrium sulfate, yttrium silicate,and yttrium oxalate. Organoyttrium complexes and yttrium metal can alsobe used. When the yttrium is to be incorporated into an electrocoat bathas a component in the pigment paste, yttrium oxide is often thepreferred source of yttrium.

The electrodepositable compositions described herein are in the form ofan aqueous dispersion. The term “dispersion” is believed to be atwo-phase transparent, translucent or opaque resinous system in whichthe resin is in the dispersed phase and the water is in the continuousphase. The average particle size of the resinous phase is generally lessthan 1.0 and usually less than 0.5 microns, often less than 0.15 micron.

The concentration of the resinous phase in the aqueous medium is oftenat least 1 percent by weight, such as from 2 to 60 percent by weight,based on total weight of the aqueous dispersion. When such compositionsare in the form of resin concentrates, they generally have a resinsolids content of 20 to 60 percent by weight based on weight of theaqueous dispersion.

The electrodepositable compositions described herein are often suppliedas two components: (1) a clear resin feed, which includes generally theactive hydrogen-containing ionic electrodepositable resin, i.e., themain film-forming polymer, the curing agent, and any additionalwater-dispersible, non-pigmented components; and (2) a pigment paste,which generally includes one or more colorants (described below), awater-dispersible grind resin which can be the same or different fromthe main-film forming polymer, and, optionally, additives such aswetting or dispersing aids. Electrodeposition bath components (1) and(2) are dispersed in an aqueous medium which comprises water and,usually, coalescing solvents.

As aforementioned, besides water, the aqueous medium may contain acoalescing solvent. Useful coalescing solvents are often hydrocarbons,alcohols, esters, ethers and ketones. The preferred coalescing solventsare often alcohols, polyols and ketones. Specific coalescing solventsinclude isopropanol, butanol, 2-ethylhexanol, isophorone,2-methoxypentanone, ethylene and propylene glycol and the monoethylmonobutyl and monohexyl ethers of ethylene glycol. The amount ofcoalescing solvent is generally between 0.01 and 25 percent, such asfrom 0.05 to 5 percent by weight based on total weight of the aqueousmedium.

In addition, a colorant and, if desired, various additives such assurfactants, wetting agents or catalyst can be included in the coatingcomposition comprising a film-forming resin. As used herein, the term“colorant” means any substance that imparts color and/or other opacityand/or other visual effect to the composition. The colorant can be addedto the composition in any suitable form, such as discrete particles,dispersions, solutions and/or flakes. A single colorant or a mixture oftwo or more colorants can be used.

Example colorants include pigments, dyes and tints, such as those usedin the paint industry and/or listed in the Dry Color ManufacturersAssociation (DCMA), as well as special effect compositions. A colorantmay include, for example, a finely divided solid powder that isinsoluble but wettable under the conditions of use. A colorant can beorganic or inorganic and can be agglomerated or non-agglomerated.Colorants can be incorporated by use of a grind vehicle, such as anacrylic grind vehicle, the use of which will be familiar to one skilledin the art.

Example pigments and/or pigment compositions include, but are notlimited to, carbazole dioxazine crude pigment, azo, tnonoazo, disazo,naphthol AS, salt type (lakes), benzimidazolone, condensation, metalcomplex, isoindolinone, isoindoline and polycyclic phthalocyanine,quinacridone, perylene, perinone, diketopyrrolo pyrrole, thioindigo,anthraquinone, indanthrone, anthrapyrimidine, flavanthrone, pyranthrone,anthanthrone, dioxazine, triarylcarbonium, quinophthalone pigments,diketo pyrrolo pyrrole red (“DPPBO red”), titanium dioxide, carbon blackand mixtures thereof The terms “pigment” and “colored filler” can beused interchangeably.

Example dyes include, but are not limited to, those that are solventand/or aqueous based such as phthalo green or blue, iron oxide, bismuthvanadate, anthraquinone, perylene, aluminum and quinacridone.

Example tints include, but are not limited to, pigments dispersed inwater-based or water miscible carriers such as AQUA-CHEM 896commercially available from Degussa, Inc., CHARISMA COLORANTS andMAXITONER INDUSTRIAL COLORANTS commercially available from AccurateDispersions division of Eastman Chemical, Inc.

As noted above, the colorant can be in the form of a dispersionincluding, but not limited to, a nanoparticle dispersion. Nanoparticledispersions can include one or more highly dispersed nanoparticlecolorants and/or colorant particles that produce a desired visible colorand/or opacity and/or visual effect. Nanoparticle dispersions caninclude colorants such as pigments or dyes having a particle size ofless than 150 nm, such as less than 70 nm, or less than 30 nm.Nanoparticles can be produced by milling stock organic or inorganicpigments with grinding media having a particle size of less than 0.5 mm.Example nanoparticle dispersions and methods for making them areidentified in U.S. Pat. No. 6,875,800 B2, which is incorporated hereinby reference. Nanoparticle dispersions can also be produced bycrystallization, precipitation, gas phase condensation, and chemicalattrition (i.e., partial dissolution). In order to minimizere-agglomeration of nanoparticles within the coating, a dispersion ofresin-coated nanoparticles can be used. As used herein, a “dispersion ofresin-coated nanoparticles” refers to a continuous phase in which isdispersed discreet “composite microparticles” that comprise ananoparticle and a resin coating on the nanoparticle. Exampledispersions of resin-coated nanoparticles and methods for making themare identified in United States Patent Application Publication2005-0287348 A1, filed Jun. 24, 2004, U.S. Provisional Application No.60/482,167 filed Jun. 24, 2003, and U.S. patent application Ser. No.11/337,062, filed Jan. 20, 2006, which is also incorporated herein byreference.

Example special effect compositions that may be used include pigmentsand/or compositions that produce one or more appearance effects such asreflectance, pearlescence, metallic sheen, phosphorescence,fluorescence, photochromism, photosensitivity, thermochromism,goniochromism and/or color-change. Additional special effectcompositions can provide other perceptible properties, such as opacityor texture. In certain embodiments, special effect compositions canproduce a color shift, such that the color of the coating changes whenthe coating is viewed at different angles. Example color effectcompositions are identified in U.S. Pat. No. 6,894,086, incorporatedherein by reference. Additional color effect compositions can includetransparent coated mica and/or synthetic mica, coated silica, coatedalumina, a transparent liquid crystal pigment, a liquid crystal coating,and/or any composition wherein interference results from a refractiveindex differential within the material and not because of the refractiveindex differential between the surface of the material and the air.

In certain embodiments, a photosensitive composition and/or photochromiccomposition, which reversibly alters its color when exposed to one ormore light sources, can be used. Photochromic and/or photosensitivecompositions can be activated by exposure to radiation of a specifiedwavelength. When the composition becomes excited, the molecularstructure is changed and the altered structure exhibits a new color thatis different from the original color of the composition. When theexposure to radiation is removed, the photochromic and/or photosensitivecomposition can return to a state of rest, in which the original colorof the composition returns. In certain embodiments, the photochromicand/or photosensitive composition can be colorless in a non-excitedstate and exhibit a color in an excited state. Full color-change canappear within milliseconds to several minutes, such as from 20 secondsto 60 seconds. Example photochromic and/or photosensitive compositionsinclude photochromic dyes.

In certain embodiments, the photosensitive composition and/orphotochromic composition can be associated with and/or at leastpartially bound to, such as by covalent bonding, a polymer and/orpolymeric materials of a polymerizable component. In contrast to somecoatings in which the photosensitive composition may migrate out of thecoating and crystallize into the substrate, the photosensitivecomposition and/or photochromic composition associated with and/or atleast partially bound to a polymer and/or polymerizable component inaccordance with certain embodiments of the present invention, haveminimal migration out of the coating. Example photosensitivecompositions and/or photochromic compositions and methods for makingthem are identified in U.S. application Ser. No. 10/892,919 filed Jul.16, 2004, incorporated herein by reference.

In general, the colorant can be present in the coating composition inany amount sufficient to impart the desired visual and/or color effect.The colorant may comprise from 1 to 65 weight percent, such as from 3 to40 weight percent or 5 to 35 weight percent, with weight percent basedon the total weight of the composition.

After deposition, the coating is often heated to cure the depositedcomposition. The heating or curing operation is often carried out at atemperature in the range of from 120 to 250° C., such as from 120 to190° C., for a period of time ranging from 10 to 60 minutes. In certainembodiments, the thickness of the resultant film is from 10 to 50microns.

As will be appreciated by the foregoing description, the presentinvention is directed to compositions for treating a metal substrate.These compositions comprise: (a) a group IIIB and/or IVB metal; (b) anelectropositive metal; (c) free fluorine; (d) a source of aluminum ions;and (e) water. The composition, in certain embodiments, is substantiallyfree of heavy metal phosphate, such as zinc phosphate, and chromate.

In yet other respects, the present invention is directed to compositionsfor treating a metal substrate that comprise: (a) a group IIIB and/orIVB metal; (b) 0.1 to 300 ppm of free fluorine; (c) a source of aluminumions; and (d) water. These compositions of the present invention aresubstantially free of phosphate ions and chromate.

As has been indicated throughout the foregoing description, the methodsand coated substrates of the present invention do not, in certainembodiments, include the deposition of a crystalline phosphate, such aszinc phosphate, or a chromate. As a result, the environmental drawbacksassociated with such materials can be avoided. Nevertheless, the methodsof the present invention have been shown to provide coated substratesthat are, in at least some cases, resistant to corrosion at a levelcomparable to, in some cases even superior to, methods wherein suchmaterials are used. This is a surprising and unexpected discovery of thepresent invention and satisfies a long felt need in the art.

Illustrating the invention are the following examples that are not to beconsidered as limiting the invention to their details. All parts andpercentages in the examples, as well as throughout the specification,are by weight unless otherwise indicated.

EXAMPLES

Fluoride ion concentration, including both free and total fluoride, canbe measured using a variety of methods familiar to those skilled in theart. Frequently, fluoride ion concentration is measured using anion-selective electrode (“ISE”), such as the sympHony® Fluoride IonSelective Combination Electrode supplied by VWR International, orsimilar electrodes. The fluoride ISE is standardized by immersing theelectrode into solutions of known fluoride concentration and recordingthe reading in millivolts; then, plotting these millivolt readings in alogarithmic graph. The millivolt reading of an unknown sample can thenbe compared to this calibration graph and the concentration of fluoridedetermined. Alternatively, the fluoride ISE can be used with a meterthat will perform the calibration calculations internally and thus,after calibration, the concentration of the unknown sample can be readdirectly.

Fluoride ion is a small negative ion with a high charge density, so inaqueous solution it is frequently complexed with metal ions having ahigh positive charge density, such as zirconium or titanium, or withhydrogen ion. The fluoride ions thus complexed are not measurable withthe fluoride ISE unless the solution they are present in is mixed withan ionic strength adjustment buffer that releases the fluoride ions fromsuch complexes. At that point the fluoride ions are measurable by thefluoride ISE, and the measurement is known as “total fluoride”. Afluoride measurement taken without using such a reagent is known as“free fluoride”, since it is only the fluoride ion not bound withhydrogen ion or in metal complexes.

For purposes of the Examples that follow, the fluoride was measured asfollows: The calibration standards were prepared by adding 2 mL each ofstandard solutions containing, respectively, 100 ppm, 300 ppm and 1000ppm of fluoride ion, to 50 mL of an ionic strength adjustment buffercomprised of 10% by weight sodium citrate dihydrate (available fromAldrich Chemical, Milwaukee, Wis.) in deionized water. The millivoltreading of each of these standards were then measured with a fluorideISE and used to construct a calibration curve as described above. Fortotal fluoride values, 2 mL of the unknown solution was mixed with 50 mLof the sodium citrate buffer and the millivolt reading of the fluorideISE of this solution was compared with the calibration curve generatedto determine the total fluoride. Free fluoride was determined bydirectly reading the millivolts of the sample solution and comparingwith the calibration curve, and then dividing this number by 26 (thedivision was necessary since the standards were diluted by a factor of26 due to the ionic strength adjustment buffer, and the free fluoridesample was not).

Example 1

An 8 liter zirconium pretreatment bath was prepared using 7 grams of 45%Hexafluorozirconic acid (available from Honeywell, Inc.) and 0.87 g of acopper nitrate solution (Cu(NO₃)₂·2½H₂O, available from FisherScientific). The bath pH was adjusted to 4.5 with Chemfil Buffer(available from PPG Industries) and heated to 100° F. (about 37.8° C.).The free fluoride of this pretreatment bath was measured at 20 ppm. Aclean cold rolled steel panel was immersed in the pretreatment bath fortwo minutes, then rinsed with deionized water and dried. The zirconiumpretreatment was measured on an XMet 3000 TX portable XRF (X-rayfluorescence) instrument that had been calibrated to measure approximatezirconium oxide thickness, and was found to be 70 nm.

To the zirconium pretreatment bath were added 12 g of Chemfos AFL, afree fluoride adjustment product (available from PPG Industries). ThepH, which had dropped to 3.9 by the chemical addition, was adjusted backto 4.5 with addition of Chemfil Buffer. The free fluoride was measuredat 114 ppm. A second clean steel panel was treated for two minutes andrinsed and dried. This panel was measured by the XMet XRF instrument andfound to have 34 nm of zirconium oxide pretreatment.

Another 12 g addition of Chemfos AFL added to the bath. The pH wasadjusted back to 4.5, and the free fluoride now measured 211 ppm. Aclean steel panel treated for two minutes, rinsed and dried, nowmeasured 22 nm of zirconium pretreatment thickness.

Another 12 g addition of Chemfos AFL, followed by subsequent pHadjustment to 4.5, increased the free fluoride to 297 ppm. A fourthsteel panel was processed through this bath as previously described;this panel was measured at 11 nm.

Yet another addition of Chemfos AFL, followed by pH adjustment,increased the measured free fluoride to 430 ppm. A cleaned steel panelprocessed through the pretreatment bath at these conditions as describeabove measured 4 nm of zirconium pretreatment. Thus, subsequentadditions of free fluoride added artificially to the zirconiumpretreatment bath caused the inhibition of zirconium pretreatmentformation on the steel panels. Zirconium pretreatments such as thoseformed at the free fluoride levels of 211 ppm and higher, would provideunacceptable corrosion resistance.

A solution of was prepared to contain 18 g/L of aluminum ion bydissolving 250 g of an aluminum nitrate solution (Al(NO₃)₃·9H₂O) into 1L of total solution volume. This solution (the “aluminum solution”, asdescribed in subsequent paragraphs of this Example) was then introducedincrementally into the zirconium pretreatment bath. A 32 mL aliquot ofthe 18 g/L aluminum solution was added to the bath to give a nominalaluminum concentration of 48 ppm. The pH, which dropped to 4.3 uponaddition of the aluminum solution, was adjusted to 4.5 with Chemfilbutter. The free fluoride was measured at 274, and a cleaned steel paneltreated for two minutes measured 22 nm of zirconium pretreatmentthickness.

Another 31 mL of 18 g/L aluminum solution was added to the zirconiumpretreatment bath, to give a nominal aluminum concentration of 94 ppm.The pH of the solution, which dropped to 4.3 upon addition of thealuminum solution, was adjusted to pH 4.5 with Chemfil Buffer. The freefluoride of this solution was measured at 154 ppm. A clean steel paneltreated in this bath for two minutes as described above measured 32 nmof zirconium coating thickness.

Another 32 mL addition of the aluminum solution was made to thezirconium pretreatment bath, to give a nominal total of 142 ppmaluminum. The pretreatment bath pH was 4.5, and the free fluoride wasmeasured at 34 ppm. A cleaned steel panel treated in the pretreatmentbath as described above was measured at 62 nm of zirconium pretreatmentthickness.

Thus, simulated bath aging of the zirconium pretreatment bath by theaddition of free fluoride caused decreased zirconium pretreatmentcoating thickness, and the addition of soluble aluminum as the nitratereturned the performance of the bath to its initial condition.

Example 2

A 4 L zirconium pretreatment bath was prepared to contain 175 ppmzirconium (from fluorozirconic acid) and 20 ppm copper (from coppernitrate). The pH of the pretreatment bath was adjusted to 4.6 withChemfil Buffer.

Next, metal panels were prepared for pretreatment in the zirconiumpretreatment bath. The metal panels to be treated were 4″×6″ panelspurchased from ACT Laboratories, Inc. Before treating in the zirconiumpretreatment bath, the panels were cleaned in a solution of Chemkleen166HP, an alkaline cleaner available from PPG Industries, preparedaccording to the manufacturer's instructions, and then rinsed withdeionized water. After the rinsing step, the panels were treated in thezirconium pretreatment bath for two minutes at 80° F. (about 26.7° C.)with mild agitation provided by an overhead mixer. Panels were processedtwo at a time. The composition of the panels processed in each group oftwenty panels was 18 electrogalvanized steel panels, one cold rolledsteel panel, and one aluminum alloy 6111 panel.

After each twenty panels, the chemical components of the bath weretested and the bath replenished using Zircobond R1, a zirconiumpretreatment replenishment product available from PPG Industries. The pHwas adjusted to 4.4 -4.5 as necessary with Chemfil Buffer and freefluoride was measured. The bath was then adjusted with aluminum ion asnecessary to maintain it between 40 and 70 ppm free fluoride. In thisExample, the free fluoride was adjusted with an aluminum sulfatesolution containing 4.4% by weight of aluminum (sold commercially asLiquid Alum, available from General Chemical), The process was continueduntil a total of 300 panels had been processed.

The fluoride control information appears in Table 1, below.

TABLE 1 Free Aluminum New Free Panels Fluoride sulfate solution Fluoridetreated (ppm) added (grams) (ppm) 0 22 — — 20 46 — — 40 65 — — 60 780.78 60 80 64 — — 100 98 1.64 53 120 75 0.65 57 140 77 0.73 60 160 800.9  58 180 71 0.48 61 200 78 0.77 55 220 71 0.48 63 240 80 0.87 63 26078 0.78 63 280 73 0.57 62 300 80 0.86 61

Example 2 confirms that aluminum sulfate acts to control free fluoridelevels in a pretreatment bath, similar to aluminum nitrate as describedabove in Example 1.

It will be appreciated by those skilled in the art that changes could bemade to the embodiments described above without departing from the broadinventive concept thereof. It is understood, therefore, that thisinvention is not limited to the particular embodiments disclosed, but itis intended to cover modifications which are within the spirit and scopeof the invention, as defined by the appended claims.

1. A pretreatment composition for treating a metal substrate comprising:(a) a group IIIB and/or IVB metal; (b) an electropositive metal; (c)free fluorine; (d) a source of aluminum ions; and (e) water, wherein thesource of aluminum ions is supplied in an amount sufficient to maintainthe level of free fluorine in the composition to no less than 0.1 ppmand no more than 750 ppm.
 2. The pretreatment composition of claim 1,wherein the source of aluminum ions comprises a water soluble aluminumcompound comprising one or more of aluminum sulfate, ammonium aluminumsulfate, potassium aluminum sulfate, sodium aluminum sulfate, aluminumnitrate, aluminum chloride, aluminum acetate, aluminum citrate, aluminumbromide, aluminum bromate, aluminum lactate, aluminum chlorate, aluminumtartrate, aluminum thiocyanate, aluminum hydroxychloride, aluminumformate, aluminum hydroxyacetate, aluminum malate, aluminum succinate,aluminum gluconate, aluminum glutamate, aluminum glycinate, aluminumfumarate, and their respective hydrated forms.
 3. The pretreatmentcomposition of claim 1, wherein the source of aluminum ions comprisesone or more of aluminum oxide, aluminum hydroxide, aluminumferricyanide, aluminum phosphate, aluminum silicate, aluminum-containingclays, aluminum-containing zeolites, aluminum soaps and salts ofaluminum-containing fatty acids.
 4. The pretreatment composition ofclaim 1, wherein the source of aluminum ions is complexed with anorganic compound.
 5. The pretreatment composition of claim 4, whereinthe organic compound comprises one or more of a polycarboxylic acid oran aminopolycarboxylic acid.
 6. The pretreatment composition of claim 1,wherein the group IIIB and/or IVB metal is present in the pretreatmentcomposition in an amount of at least 100 ppm metal.
 7. The pretreatmentcomposition of claim 1, wherein the electropositive metal is included inthe pretreatment composition in an amount of at least 1 ppm of totalmetal measured as elemental metal.
 8. The pretreatment composition ofclaim 1, wherein the pretreatment composition is substantially free ofphosphate ions.
 9. The pretreatment composition of claim 1, wherein thepretreatment composition is substantially free of chromate and/or zincphosphate.
 10. A method for treating a metal substrate comprisingcontacting the substrate with a pretreatment composition comprising: (i)a group IIIB and/or IVB metal; (ii) an electropositive metal; (iii) freefluorine; (iv) a source of aluminum ions; and (v) water, wherein thesource of aluminum ions is supplied in an amount sufficient to maintainthe level of free fluorine in the pretreatment composition to no lessthan 0.1 ppm and no more than 750 ppm.
 11. The method of claim 10,further comprising cleaning the metal substrate prior to the contactingstep.
 12. The method of claim 10, wherein the source of aluminum ions(iv) comprises a water soluble aluminum compound comprising one or moreof aluminum sulfate, ammonium aluminum sulfate, potassium aluminumsulfate, sodium aluminum sulfate, aluminum nitrate, aluminum chloride,aluminum acetate, aluminum citrate, aluminum bromide, aluminum bromate,aluminum lactate, aluminum chlorate, aluminum tartrate, aluminumthiocyanate, aluminum hydroxychloride, aluminum formate, aluminumhydroxyacetate, aluminum malate, aluminum succinate, aluminum gluconate,aluminum glutamate, aluminum glycinate, aluminum fumarate, and theirrespective hydrated forms.
 13. The method of claim 10, wherein thesource of aluminum ions (iv) comprises one or more of aluminum oxide,aluminum hydroxide, aluminum ferricyanide, aluminum phosphate, aluminumsilicate, aluminum-containing clays, aluminum-containing zeolites,aluminum soaps and salts of aluminum-containing fatty acids.
 14. Themethod of claim 10, wherein the group IIIB and/or IVB metal (i) ispresent in the pretreatment composition in an amount of at least 100 ppmmetal.
 15. The method of claim 10, wherein the electropositive metal(ii) is included in the pretreatment composition in an amount of atleast 1 ppm of total metal measured as elemental metal.
 16. The methodof claim 10, wherein the source of aluminum ions is complexed with anorganic compound.
 17. The method of claim 16, wherein the organiccompound comprises one or more of a polycarboxylic acid or anaminopolycarboxylic acid.
 18. The method of claim 10, further comprisingcontacting the pretreated substrate with a coating compositioncomprising a film-forming resin, wherein the contacting comprises anelectrocoating step wherein an electrodepositable composition isdeposited onto the pretreated substrate by electrodeposition.
 19. Ametal substrate treated according to the method of claim 10.